The invention relates to a filtering apparatus, comprising an inlet channel for the flow to be filtered, an outlet channel for the filtered flow, a number of parallel filtering elements, into which the flow to be filtered may be directed so that the infiltration occurs out of the element through the element jacket, and at least one rotating washing organ connecting alternately to different elements for forming an outlet channel for the backflushing of elements generated with the pressure of the filtered flow. Further, the invention relates to a method for washing the filtering elements of the apparatus.
A filtering device is needed especially in motors as a fuel or luboil filter, with the continuous backflushing of which the operation of the motor is ensured in long-term continuous use. The apparatus typically comprises a large number of filtering elements, the main part of which is continuously in operation while the washing is conducted in one or several elements at a time, depending on the number of washing arms.
A state-of-the art backflushable filtering apparatus has been described in the patent publication DE-4 340 275. The apparatus comprises parallel, candle-shaped filtering elements arranged around a vertical axle as two nested rings. The flow to be filtered is directed into the elements from their upper and lower ends, and the infiltration occurs out of the element through the cylindrical jacket of each element. For backwashing the elements, a washing organ consisting of two washing arms of different lengths is arranged below them, the arms being fastened to the rotatable vertical axle of the apparatus. The washing arms are arranged to alternately connect to the lower ends of different filtering elements so that they form outlet channels for the washing flow. Corresponding to the washing arms, closers are attached to the rotating axle of the apparatus above the filtering elements, the closers closing the upper end of the filtering element in question for the duration of the washing stage, thus preventing the flow to be filtered from mixing with the washing flow.
According to the publication DE-4 340 275, the rotating movement of the vertical axle of the apparatus and the washing arms is achieved with the help of a turbine rotor arranged in the inlet channel of the flow to be filtered and with cogwheels connected to it and acting as a transmission mechanism. The movement of the washing arms is thus maintained by the motion energy of the flow coming into the apparatus.
The drawback of the solution in the publication DE-4 340 275 is that the rotation of the washing arms is dependent on the flow rate of the flow to be filtered coming into the apparatus, which may vary. If the flow rate is too high, it makes the washing arms to rotate too fast, and the washing periods of the filtering elements remain too short; and again, if the flow rate is too low, the washing arms rotate too slowly from one element to the other, or they stop altogether, if the decelerated flow cannot rotate the turbine rotor any more. The rotation of the washing arms is hindered by the rotor and the transmission mechanism getting dirty, and due to the structure of the apparatus, it is difficult to service the mechanism.
The object of the invention is to provide a solution, in which the axle of the apparatus and one or several washing organs are rotated by utilising the flow pressure present in the apparatus so that the drawbacks associated with the state-of-the art technology can be avoided. It is characteristic of the filtering apparatus of the invention that a freewheel clutch is connected to the rotating axle of the washing organ, which converts the reciprocating motion generated by the pressure of the flow present in the apparatus and by the lower pressure alternating with it into a continuously parallel, stepping rotary motion of the washing organ.
According to the invention, the rotation of the washing organ and the washing periods in different filtering elements are generated with a pressure difference, which it is possible to keep substantially constant, or which varies less than the flow rate of the flow coming into the apparatus. This ensures that the sufficiently long washing periods are repeated with a suitable frequency in all filtering elements of the apparatus.
A substantial advantage of a second solution of the invention is that the freewheel clutch may be arranged outside the filtering room of the apparatus, connected to the rotating axle, so that it is easy to service the freewheel clutch and other organs maintaining the rotating movement, and the service may be carried out while the filtering continues.
The freewheel clutch may consist of an actuator driving the rotating axle of the washing organ, which is alternately in sliding contact with the axle and which alternately locks into it so that the axle rotates along with the organ. The movement of the actuator may be generated, for example, by articulating it to a piston reciprocating on the alternating pressure.
The pressure of the filtered flow is especially advantageously used for rotating the washing organ, by arranging the said flow to influence the said piston or another organ driving the freewheel clutch. The filtered flow is pure, so that it contaminates the rotating mechanism substantially less than an unfiltered flow. The apparatus of the invention preferably comprises channels and related control valves for connecting the pressure of the filtered flow and the lower counterpressure alternately to different sides of the piston.
The lower pressure opposite the said pressure of the filtered flow may be the pressure prevailing in the outlet channel for the washing flow of the apparatus, to which the piston or another actuator may be connected. In the filters of a motor, the outlet channel is generally in the atmospheric pressure prevailing in the surroundings.
The solution of the invention makes it possible to hydraulically adjust the rotating movement of the washing organ so that the frequency and duration of the washing periods may be controlled with it. The movement of the washing organ may thus be damped, or it may be stopped exactly at the place of the element to be washed, in which the washing organ remains for a desired time before the movement continues.
In the method of the invention, the filtering elements are washed in the filtering apparatus, comprising an inlet channel for the flow to be filtered, an outlet channel for the filtered flow, and a number of parallel filtering elements, into which the flow to be filtered is directed so that the infiltration occurs out of the element through the element jacket. The washing is achieved by coupling alternately different filtering elements to the rotary washing organ so that the washing occurs as backflushing directed to the washing organ with the pressure of the filtered flow. Essential in the method is that the rotating axle of the washing organ is rotated continuously in the same direction in a stepping manner using a mechanism, the reciprocating movement of which is generated with the pressure of the flow in the apparatus and with the lower pressure alternating with this. The former pressure is advantageously the pressure of the clean flow filtered in the apparatus, and the lower pressure is the ambient pressure present in the washing arm.
In the method, the steps of the washing organ may be generated with a freewheel clutch, comprising an organ driving the rotating axle of the washing organ, which is alternately in sliding contact with the axle and which alternately locks into it for rotating the axle, the said organ being moved with a piston articulated with it, the piston being reciprocated by coupling the said pressures of different sizes alternately to its different sides.